Transparent heat protection element

ABSTRACT

The heat protection element comprises carrier elements, for example in the form of glass plates. In an interspace between, in each instance, two glass plates a protection layer comprising a cured polysilicate which is formed of alkali silicate and at least one curing agent is disposed. In the polysilicate, a molar ratio of silicon dioxide to alkali metal oxide is set to be greater than 4:1. The starting composition for the polysilicate is a free-flowable composition having a water content of up to 60 percent and capable of being introduced into the interspace between two carrier elements. After curing the composition, the high water content is retained and the polysilicate has nevertheless good inherent strength and adhesion on the carrier elements.

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a transparent heat protection elementcomprising at least one carrier element and one protection layercomprising hydrous alkali silicate as well as a process for thefabrication of heat protection elements.

Transparent heat protection elements of this type are known in variousimplementations and are used inter alia as structural elements. Glassplates most frequently serve as carrier elements, however, othertransparent. materials can also be used such as, for example, syntheticmaterials. Especially high requirements are made of the heat protectionof structural elements which, in the form of glazing, form boundaries ofrooms or are used for doors. From DE C3 19 00 054, heat insulatingtransparent laminated glasses are known, in which a layer comprisingdried hydrous alkali silicate is disposed between two glass surfaces.Under the influence of heat on this laminated glass, for example in theevent of fire, the intermediate layer comprising alkali silicate foamsand the water contained in the alkali silicate vaporizes. In this waythe intermediate layer becomes impermeable to heat radiation and for agiven length of time, forms effective protection against undesired heattransmission. Although at least one of the glass plates cracks andbreaks, the glass parts adhere to the expanded foam layer. To improveheat protection, several glass plates and intermediate layers comprisingalkali silicate are disposed one behind the other. In the fabrication oflaminated glasses of this type, a thin layer of alkali silicate isapplied in liquid form on one side of a glass plate, and this layer issubsequently dried by drawing off the excess water, for example, throughthe effect of heat. This drying process is expensive and requires aparticular drying time whereby the fabrication process is delayed. Thesecond glass plate must subsequently be affixed by adhesion on theintermediate or protective layer comprising alkali silicate. Themanufacture of laminated glasses of this type places high demands onproduction in order to ensure that no opaqueness of the laminated glassdue to the presence of air bubbles or other production defects, occur.

It is further known from EP A-2 192 249, to introduce the alkalisilicate of the intermediate layer in the form of a hydrogel layer withincreased water content. These hydrogel layers have a water content of80 to 90% and are therefore not self-supporting. Hydrogel layers of thistype are suggested in order to improve the optical properties of theintermediate layer. Since the hydrogel layer itself does not havesufficient cohesion or sufficient adhesion relative to the adjoiningglass layers, it is suggested to add an organic binding agent forstabilizing the layer, for example gum arabic. Adding these bindingagents is necessary in order to prevent the hydrogel from running out ofthe interspace between the laminated glasses or in the event one of theglass plates breaks. The disadvantages of the insufficient cohesion andadhesion of the hydrogel layer require additional expensive measures.The content of silicon dioxide is maximally 20 percent by weight and themolar ratio of silicon dioxide and sodium oxide as the alkali metaloxide, ranges from 2 to maximally 4.

SUMMARY OF THE INVENTION

Although these known transparent heat protection elements alreadysatisfy high requirements with respect to heat and fire protection, theyare still unsatisfactory with respect to processing and application ofthe intermediate layer comprising hydrous alkali silicate. The presentinvention is therefore based on the task of creating a transparent heatprotection element which has a high degree of transparency and ageingstability, in which the protection or intermediate layer can be producedby casting and without drying, and the protection layer has goodinherent strength as well as good adhesion on the adjoining carrierelements. The starting composition for the protection layer isfree-flowing and suitable for pouring into hollow spaces andsubsequently cures within an adequate period of time, to form theprotection layer.

This task is solved according to the invention in that the protectionlayer is a polysilicate comprising alkali silicate and a curing agent,and because the polysilicate has a molar ratio of silicon dioxide andalkali metal oxide which is greater than 4:1. A lithium, sodium orpotassium silicate, or a mixture thereof, is preferably employed as thealkali silicate and a sodium, potassium or lithium oxide, or a mixturethereof, is used as the alkali metal oxide.

Reactive silicon compounds containing silicon oxide are preferable ascuring agents, wherein preferably silicic acid or compounds which setfree silicic acid in aqueous solution are used. The use of othercompounds not containing Si as curing agents or supplementary curingagents is not excluded. Suitable are: All compounds forming no insolubleprecipitates in the reaction with alkali silicate and thereby having anegative effect on the optical properties, are preferred. These arecompounds such as inorganic and organic acids, esters, acid amides,glyoxal, alkylene carbonates, alkali carbonates and alkali hydrogencarbonates, borates, phosphates, and paraformaldehyde. These can be usedin combination with the main curing agent comprising silicic acid insmall quantities, customarily less than 5 percent, without thetransparency of the polysilicate layer being impaired.

This protective layer according to the invention comprising curedpolysilicate has good inherent strength and develops good adhesion onthe adjoining carrier elements in the form of glass plates or othertransparent structural elements. The starting composition isfree-flowing and readily castable. The cured protective layer is of highoptical quality and transparency and has good ageing stability. Thespecial properties of the protective layer in the form of the curedpolysilicate are achieved when the polysilicate layer has a silicondioxide content between 30 to 55 percent. The maximum content of alkalimetal oxide (M₂ O) in the form of sodium, potassium or lithium oxide, ora mixture thereof, is 16 percent. The cured polysilicate layer comprisesup to 60 percent water. Thus, heat protection elements with a protectivelayer according to the invention reach a very high fire resistance valuesince a relatively large quantity of water is available for thevaporization process. The high content of silicon dioxide is achieved inthat the curing agent is a silicon-containing compound, advantageouslysilicic acid or a compound splitting off silicic acid. In advantageousmanner the polysilicate layer is disposed in a transparent heatprotection element between two glass plates and forms with them alaminated element. To achieve higher heat resistance values, heatprotection elements are formed in which the heat protection elementcomprises several polysilicate layers disposed in each instance betweentwo glass plates and the glass plates and the polysilicate layers form alaminated element. In these arrangements according to the invention, thepolysilicate layers are in direct connection with the adjoining glassplates which form the carrier elements. The adhesion betweenpolysilicate layers and glass plates permits the direct formation of thelaminated elements without an additional process of affixing byadhesion, whereby the production process is significantly simplified.

The method for the production of a transparent heat protection elementusing an hydrous alkali silicate is characterized according to theinvention in that the alkali silicate is combined with a curing agentcomprising silicon dioxide or capable of setting free silicon dioxide,and a castable composition is formed. This composition is introducedinto a mould cavity or applied onto a carrier element, and subsequentlythe composition is cured to form a solid polysilicate layer whileretaining the water content. In the cured polysilicate, the molar ratioof silicon dioxie to alkali metal oxides is adjusted to a maximum ratiogreater than 4:1.

Consequently, the method according to the invention permits theconstruction of laminated elements which comprise several carrierelements disposed at a distance, one from the other, and to castsubsequently the interspace between the carrier elements with thepourable composition comprising alkali silicate and one or severalcuring agents. Due to the high water content, the composition is, to ahigh degree, free-flowing end can also be poured without difficulty intothe interspaces of laminated glazing with small distances between theglass plates. Since the composition can be cured without drying e.g.without giving off water, to form a solid polysilicate layer, the dryingprocess can be omitted, which significantly simplifies the production ofcorresponding heat protection elements. The reaction or curing time canbe accelerated by heat in known manner. The potlife of the castablecomposition at room temperature is in any case sufficiently long inorder to permit a normal course of manufacture. In the production of theheat protection elements, the composition can, as described, byintroduced or poured into a mould cavity between two carrier elements.But it is also possible to apply the composition onto a carrier elementand to subsequently place a second carrier element onto the protectivelayer while it is not yet cured, or to seal the second carrier elementwith the protective layer after it is cured. However, the latter wouldonly be useful if on conventional installations for production of theknown heat protection elements, transparent heat protection elementswith the protective layer according to the invention are to be produced.Part of the advantage in that case is still retained since no dryingprocess is necessary and the curing of the composition to form thepolysilicate layer takes place without giving off water, which means ittakes place with retention of the water content.

The composition comprising alkali silicate and curing agent ispreferably freed of gas before it is processed. It is thereby ensuredthat no gas inclusions are present in the cured polysilicate layer,which could disturb the optical quality of the heat protection elementaccording to the invention. However, the removal of the gas can alsotake place after the hollow spaces have been filled. To increase theadhesion of the polysilicate layer on the carrier elements, it ispossible to add, before processing to the composition, auxiliary meansin the form of anionic or non-ionogenic surfactants and/or the carrierlayers can be pretreated by means of this type. The carrier layers can,in a preferred manner, also be pretreated with an adhesion enhancingagent, preferably with an organo-functional silane.

As carrier elements for the transparent heat protection elementaccording to the invention, not only elements comprising glass, inparticular glass plates, are suitable, but also other materials with thedesired optical properties, as long as they meet the technical andphysical requirements, for example, of the heat resistance. Theresistance value of the heat protection layer is in any case improved bythe increased water content. Thermally or chemically prestressed glasscan also be used entirely or partially, as the carrier material.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following examples illustrate the present invention.

EXAMPLE 1

A heat protection element comprises a glazing which is assembled of fourglass panes in such a way that, a distance of 1 mm is left betweenadjacent glass panes. Along the edges of the glass panes, the narrowsides of the hollow volumes between the glass panes is sealed with asuitable sealing material around the entire circumference of the glasspanes in known manner. A filling opening is left open into each hollowspace between, in each instance, two glass panes. From an alkalisilicate in the form of a potassium silicate and colloidal silicic acid,a pourable composition is prepared which, after curing forms apolysilicate with a molar ratio of SiO₂ to K₂ O of 4.7:1. This liquidcomposition is subjected, in known manner, to a process in which gas isremoved and subsequently introduced through the filling opening into thehollow spaces between, in each instance, two glass panes. Thecomposition is free-flowing so that it can be filled in withoutdifficulties and can displace the air in the hollow spaces, withoutmixing taking place. Following the complete filling of the hollowspaces, the filling openings are also sealed. The laminated elementcomprising four glass panes and three interspaced protective layerscomprising polysilicate formed in this way, is stored in a suitableposition until the reaction process has been completed and the curedpolysilicate of the three protective layers has acquired the desiredinherent strength and adhesion on the glass plates. To accelerate thereaction the temperature is raised to 60° C. After curing of thepolysilicate is completed the laminated elements formed in this way canbe handled in any manner known for laminated glass elements and they canalso be cut into different shapes. The protective layer disposed betweenthe glass plates comprising cured polysilicate has a water content of 47percent by weight. The cured polysilicate layers disposed between theglass panes does not narrow the optical properties of the glass platelaminate in any manner, and the heat protection element produced in thisway is distinguished by optimum fire resistance properties.

EXAMPLE 2

In a modified variant according to Example 1, a filling composition wasused in which a mixture of potassium and lithium silicate in a ratio of8.5:1.5 and a 30 percent silicic acid dispersion in water in aquantitative ratio, was allowed to react so that a K-Li polysilicatewith a molar ratio of SiO₂ to (K₂ O+Li₂ O) of 5.0:1, was obtained.Before filling in this composition, an agent in the form of a polyol forlowering the freezing point by 15 percent, was added. The water contentof the cured polysilicate was 51.2 percent by weight. The fireresistance properties were practically identical to those of the elementin Example 1.

EXAMPLE 3

In a varied embodiment of Examples 1 and 2, 35 mol percent of thepotassium ion are replaced by sodium and as the curing agent, a hydratedprecipitated silicic acid having a water content of 21 percent is used.The water content of the cured polysilicate is 44 percent by weight. Themolar ratio of SiO₂ to (K₂ O+Li₂ O+Na₂ O) is here also 5.0:1.

We claim:
 1. Transparent heat protection element comprising at least onetransparent carrier element and one transparent protective layercomprising hydrous alkali silicate in direct connection with saidtransparent carrier element, characterized in that the protection layeris a cured but not dried polysilicate formed by a combination of alkalisilicate, at least about 44 to 60 percent by weight water and at leastone curing agent, and that in the polysilicate, a molar ratio of silicondioxide to alkali metal oxide is greater than 4:1, the curedpolysilicate containing substantially all water that was present in thecombination of alkali silicate and curing agent.
 2. Heat protectionelement as claimed in claim 1, wherein the curing agent is silicic acidor a compound which sets free silicic acid.
 3. Heat protection elementas stated in claim 1, characterized in that the alkali silicate is alithium, sodium or potassium silicate or a mixture thereof.
 4. Heatprotection element as stated in claim 1, characterized in that thealkali metal oxide is a sodium, potassium or lithium oxide or a mixturethereof.
 5. Heat protection element as stated in claim 1, characterizedin that the polysilicate layer comprises from 30 to 55 percent silicondioxide.
 6. Heat protection element as stated in claim 1, characterizedin that the polysilicate layer comprises maximally 16 percent alkalimetal oxide.
 7. Heat protection element as stated in claim 1,characterized in that the polysilicate layer comprises a means forlowering the freezing point of the water.
 8. Heat protection element asstated in claim 1, characterized in that the curing agent is a compoundcomprising silicon oxide.
 9. Heat protection element as stated in claim5, characterized in that the curing agent is silicic acid or a compoundsplitting off silicic acid.
 10. Heat protection element as stated inclaim 8, including an additional curing agent selected from the groupconsisting of inorganic or organic acids, esters, acid amides, glyoxal,alkylene carbonates, alkali carbonates and alkali hydrogen carbonates,borates, phosphates or paraformaldehyde.
 11. Heat protection element asstated in claim 1, characterized in that the polysilicate layer isdisposed between two glass plates and forms with them a laminatedelement.
 12. Heat protection element as stated in claim 1, characterizedin that the heat protection element comprises a plurality ofpolysilicate layers alternating with and being disposed between aplurality of glass plates and that the glass plates and the polysilicatelayers form a laminated element.
 13. Heat protection element as statedin claim 7, wherein the means for lowering the freezing point of thewater comprises a polyol.
 14. Method for the production of a transparentheat protection element using a hydrous alkali silicate, comprising:combining an alkali silicate with a curing agent that includes or setsfree silicon dioxide, to form a pourable free-flowing composition havingan initial water content of at least about 44 to 60 percent by weight;adjusting the amounts of alkali silicate and curing agent so that amolar ratio of silicon dioxide to alkali metal oxides in a curedpolysilicate to be formed, is greater than 4:1; introducing the pourablecomposition into a mould cavity between two transparent carrierelements; subsequently and without a drying step, allowing thecomposition, while retaining all of the initial water content, to cureto form a solid polysilicate layer without drying, said polysilicatelayer being in direct connection with said transparent carrier elements,the molar ratio of silicon dioxide to alkali metal oxides in the curedand not dried polysilicate layer, being a ratio greater than 4:1 and theinitial water content remaining in the layer.
 15. Method as stated inclaim 14, including freeing the pourable composition of gas beforeintroducing the pourable composition into the mould cavity.
 16. Methodas stated in claim 14, wherein the carrier elements have surfaces, themethod including adding an anionic or non-ionogenic surfactant to atleast one of the pourable composition and the surfaces of the carrierelements for increasing an adhesion between the polysilicate layer andthe carrier elements.
 17. Method as stated in claim 14, wherein thecarrier elements have surfaces, the method including pre-treating thesurfaces of the carrier elements with an adhesion enhancing agent in theform of an organo-functional silene.
 18. Method according to claim 14including providing silicic acid or a compound which frees silicic acidas the curing agent.